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Title: A PEG assisted sol-gel synthesis of LiFePO{sub 4} as cathodic material for lithium ion cells

Abstract

In order to obtain fine-particle LiFePO{sub 4} with excellent electrochemical performance, LiFePO{sub 4}/C powders were synthesized by a poly(ethylene glycol) (PEG) assisted sol-gel method. All samples were characterized by X-ray powder diffraction and scanning electron microscopy, and their electrochemical properties were investigated by cycle voltammograms and charge-discharge tests. The sample, synthesized with the n {sub PEG}/n {sub LFP} = 1:1 under sintering temperature of 600 deg. C, possesses the global morphology and particle size of about 100 nm. This sample delivers the first discharge capacity of 162 mAh g{sup -1}, i.e. 95.3% of the theoretical capacity, at the 15 mA g{sup -1} discharge current between 2.5 and 4.0 V (versus Li/Li{sup +}). The sample also displays a robust rate capability and stable cycle-life. The improved electrochemical performance originates mainly from the fine particle of nanometric dimension, regular global morphology and uniform dispersing in the product as well as the increased electronic conductivity by carbon coating.

Authors:
 [1];  [1];  [2];  [3]
  1. College of Chemistry, Sichuan University, Chengdu, Sichuan 610064 (China)
  2. College of Chemistry, Sichuan University, Chengdu, Sichuan 610064 (China). E-mail: laiqy5@hotmail.com
  3. Analytical and Testing Center, Sichuan University, Chengdu, Sichuan 610064 (China)
Publication Date:
OSTI Identifier:
21000636
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 42; Journal Issue: 5; Other Information: DOI: 10.1016/j.materresbull.2006.08.018; PII: S0025-5408(06)00347-3; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CARBON; ELECTROCHEMISTRY; INORGANIC COMPOUNDS; IONIC CONDUCTIVITY; LITHIUM IONS; MORPHOLOGY; PARTICLE SIZE; PERFORMANCE; POLYETHYLENE GLYCOLS; SCANNING ELECTRON MICROSCOPY; SINTERING; SOL-GEL PROCESS; X-RAY DIFFRACTION

Citation Formats

Xu Zhihui, Xu Liang, Lai Qiongyu, and Ji Xiaoyang. A PEG assisted sol-gel synthesis of LiFePO{sub 4} as cathodic material for lithium ion cells. United States: N. p., 2007. Web.
Xu Zhihui, Xu Liang, Lai Qiongyu, & Ji Xiaoyang. A PEG assisted sol-gel synthesis of LiFePO{sub 4} as cathodic material for lithium ion cells. United States.
Xu Zhihui, Xu Liang, Lai Qiongyu, and Ji Xiaoyang. Thu . "A PEG assisted sol-gel synthesis of LiFePO{sub 4} as cathodic material for lithium ion cells". United States. doi:.
@article{osti_21000636,
title = {A PEG assisted sol-gel synthesis of LiFePO{sub 4} as cathodic material for lithium ion cells},
author = {Xu Zhihui and Xu Liang and Lai Qiongyu and Ji Xiaoyang},
abstractNote = {In order to obtain fine-particle LiFePO{sub 4} with excellent electrochemical performance, LiFePO{sub 4}/C powders were synthesized by a poly(ethylene glycol) (PEG) assisted sol-gel method. All samples were characterized by X-ray powder diffraction and scanning electron microscopy, and their electrochemical properties were investigated by cycle voltammograms and charge-discharge tests. The sample, synthesized with the n {sub PEG}/n {sub LFP} = 1:1 under sintering temperature of 600 deg. C, possesses the global morphology and particle size of about 100 nm. This sample delivers the first discharge capacity of 162 mAh g{sup -1}, i.e. 95.3% of the theoretical capacity, at the 15 mA g{sup -1} discharge current between 2.5 and 4.0 V (versus Li/Li{sup +}). The sample also displays a robust rate capability and stable cycle-life. The improved electrochemical performance originates mainly from the fine particle of nanometric dimension, regular global morphology and uniform dispersing in the product as well as the increased electronic conductivity by carbon coating.},
doi = {},
journal = {Materials Research Bulletin},
number = 5,
volume = 42,
place = {United States},
year = {Thu May 03 00:00:00 EDT 2007},
month = {Thu May 03 00:00:00 EDT 2007}
}
  • This research has been done on the synthesis of carbon coated LiFePO{sub 4} through sol-gel process. Carbon layer serves for improving electronic conductivity, while the variation of pH in the sol-gel process is intended to obtain the morphology of the material that may improve battery performance. LiFePO{sub 4}/C precursors are Li{sub 2}CO{sub 3}, NH{sub 4}H{sub 2}PO{sub 4} and FeC{sub 2}O{sub 4}.H{sub 2}O and citric acid. In the synthesis process, consisting of a colloidal suspension FeC{sub 2}O{sub 4}.H{sub 2}O and distilled water mixed with a colloidal suspension consisting of NH{sub 4}H{sub 2}PO{sub 4}, Li{sub 2}CO{sub 3}, and distilled water. Variations additionmore » of citric acid is used to control the pH of the gel formed by mixing two colloidal suspensions. Sol in this study had a pH of 5, 5.4 and 5.8. The obtained wet gel is further dried in the oven and then sintered at a temperature 700°C for 10 hours. The resulting material is further characterized by XRD to determine the phases formed. The resulting powder morphology is observed through SEM. Specific surface area of the powder was tested by BET, while the electronic conductivity characterized with EIS.« less
  • Graphical abstract: Discharge capacity versus cycle number of Li{sub 4}Ti{sub 5}O{sub 12} samples synthesized by (a) CTAB-assisted sol-gel and (b) normal sol-gel method. Highlights: {yields} CTAB-assisted sol-gel route for the synthesis of nano-size Li{sub 4}Ti{sub 5}O{sub 12}. {yields} CTAB directs the microstructure of the gels and helps to control the particle size of Li{sub 4}Ti{sub 5}O{sub 12}. {yields} Li{sub 4}Ti{sub 5}O{sub 12} exhibits promising cycling performance with initial capacity of 174 mAh g{sup -1} and sustains {approx}94% beyond 30 cycles. -- Abstract: A simple CTAB-assisted sol-gel technique for synthesizing nano-sized Li{sub 4}Ti{sub 5}O{sub 12} with promising electrochemical performance as anodemore » material for lithium ion battery is reported. The structural and morphological properties are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemical performance of both samples (with and without CTAB) calcined at 800 {sup o}C is evaluated using Swagelok{sup TM} cells by galvanostatic charge/discharge cycling at room temperature. The XRD pattern for sample prepared in presence of CTAB and calcined at 800 {sup o}C shows high-purity cubic-spinel Li{sub 4}Ti{sub 5}O{sub 12} phase (JCPDS no. 26-1198). Nanosized-Li{sub 4}Ti{sub 5}O{sub 12} calcined at 800 {sup o}C in presence of CTAB exhibits promising cycling performance with initial discharge capacity of 174 mAh g{sup -1} ({approx}100% of theoretical capacity) and sustains a capacity value of 164 mAh g{sup -1} beyond 30 cycles. By contrast, the sample prepared in absence of CTAB under identical reaction conditions exhibits initial discharge capacity of 140 mAh g{sup -1} (80% of theoretical capacity) that fades to 110 mAh g{sup -1} after 30 cycles.« less
  • Nano-sized particles of spinel LiMn{sub 2}O{sub 4} and LiCr{sub x}Mn{sub 2-x}O{sub 4} (x = Cr; 0.00-0.40) have been synthesized using phthalic acid as chelating agent for the first time by sol-gel method. When compared to solid-state synthesis method, the sol-gel route reduces heating time of synthesize and to obtain particles of uniform surface morphology. The synthesized samples were characterized through thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images of the parent compounds show nanospherical grains of LiMn{sub 2}O{sub 4} when compared to chromium-doped ones. XRD patterns of LiMn{sub 2}O{sub 4} ascertainmore » amorphous nature and for high calcined LiCr{sub x}Mn{sub 2-x}O{sub 4} single phase highly crystalline patterns were obtained. TEM images of the parent and chromium-doped spinel particles depict individual grain morphology with well-separated grain boundaries. LiCr{sub 0.10}Mn{sub 1.90}O{sub 4} excels in discharge and cycling behaviour and offer higher columbic efficiency, when compared to un-doped LiMn{sub 2}O{sub 4}. Cyclic voltammograms of LiMn{sub 2}O{sub 4} and LiCr{sub x}Mn{sub 2-x}O{sub 4} exhibit oxidation and reduction peaks corresponding to Mn{sup 3+}/Mn{sup 4+} and Cr{sup 3+}/Cr{sup 4+}.« less
  • LiFePO{sub 4}, Li{sub 0.98}Mg{sub 0.01}FePO{sub 4}, and Li{sub 0.96}Ti{sub 0.01}FePO{sub 4} were synthesized via a sol-gel method, using a variety of processing conditions. For comparison, LiFePO{sub 4} was also synthesized from iron acetate by a solid state method. The electrochemical performance of these materials in lithium cells was evaluated and correlated to mean primary particle size and residual carbon structure in the LiFePO{sub 4} samples, as determined by Raman microprobe spectroscopy. For materials with mean agglomerate sizes below 20 {micro}m, an association between structure and crystallinity of the residual carbon and improved utilization was observed. Addition of small amounts ofmore » organic compounds or polymers during processing results in carbon coatings with higher graphitization ratios and better electronic properties on the LiFePO{sub 4} samples and improves cell performance in some cases, even though total carbon contents remain very low (<2%). In contrast, no performance enhancement was seen for samples doped with Mg or Ti. These results suggest that it should be possible to design high power LiFePO{sub 4} electrodes without unduly compromising energy density by optimizing the carbon coating on the particles.« less
  • We report on the synthesis and preliminary characterisation by X-ray diffraction (XRD), scanning electron microscopy (SEM), Moessbauer spectroscopy and infrared spectroscopy (IR) of C-LiFePO{sub 4}. Homogeneous sub-micron sized particles of surface carbon coated phase pure LiFePO{sub 4} are synthesised by a novel non-aqueous oxalate based sol-gel procedure. Our synthetic route successfully overcomes the incidence of Fe{sup 3+}, effectively controls undesirable particle growth and has the potential for upscaling and application as Li-ion battery cathodes.